How do I tell if my bag is leaking?

A leak is sometimes hard to find.  I'm guessing that you haven't found it yet and are probably asking this question because your bagpipe has become very hard to play and you suspect a leak.

The simple answer is to remove the drones, put appropriate corks in the stocks for the drones and chanter and blow up the bag - but you've already done that. 

Actually, all bags "eventually" will deflate, so the question becomes how much leakage is acceptable and under what conditions?  (Remember that a bag is porous so that moisture can escape overnight.)

My rule of thumb is that the bagpipe should not require more than one breath in two minutes under the following conditions:

Blowstick doesn't leak. (Check it by trying to blow backwards through it.)
Cork in the chanter stock.
Small corks in the drone tops.
Blow the bag up hard.
Squeeze under arm for two minutes.

If the bagpipe leaks, then remove the drones, place corks in the drone stocks and repeat the test. 

This is a critical point: If the problem goes away, repeat the test while pulling the bass drone stock (which is probably sticking you in the chest) and the tenor drone stock (which is aimed off to your left) into their "normal" positions using masking tape or string.  If the problem is there again, you may have a grommet leak in a synthetic bag or serious wear in a "fold" or "wrinkle" in a leather/hide bag (i.e., where the material is kinked between the drones.). 

If the problem is still associated with the bag, there are several places to check (with the corks and blowstick in place):

No stock should twist in the bag.  These should be re-tied. 

Use a wet finger to "feel" for leaks where the stocks tie into the bag.  These can occur because the hole was cut too big, or the drone wasn't positioned properly during tie-in.  There should be leather above the tie-in cord all the way around.

Look for cracks/checks in the tops of the stocks. Even "little" cracks in the stocks can provide passageways for an air leak, so inspect the stocks carefully.  Repair as needed.

Be SURE that the blowstick is really holding air by listening and using a wet finger to look for leaks around the stock edges.

In a synthetic bag, if the problem is in the bag and you can't clearly find a "source", add one cup of water to the bag through a stock, and blow the bag up.   (Note: If you have a non-black bag, you can add a bit of food coloring to the water to the water to make it easier to spot the problem area.)  (Also, I cannot advise dunking a bag into a tank of water because the stocks will be exposed to water and may split.)

If water oozes out of the material under the blowstick, you can be proud of the digestive capabilities of the enzymes in your saliva - they dissolved the bag. If you are leaking at a grommet, rest assured that this is unfortunately common.

If you have a leak, you can smear silicone sealant over this part of the bag (inside or outside) as a temporary fix, but generally replacement is required.  Consider adding a tube-type water trap to collect your saliva and to avoid the problem with the next bag.  If you find a leak somewhere else, re-tie, re-clamp or replace.

In a leather bag, I'm not in favor of adding water since you'd have to re-season it afterwards.  I suggest just re-seasoning the bag and the repeat the test.  If the bag still doesn't seal, replace it.

If the problem is not in the bag, first check for leaks between the drones and their stocks.  Poor hemping jobs (or wads of teflon tape) will leak.  Then check each section of the drones.  An oval shaped tuning pin in a circular receiver (or visa versa) will leak, but, more importantly, will make the bagpipe unstable and hard to play. It may need a "$eriou$" repair.  I've also seen cracks in the tuning pins resulting from the use of "gorilla force" to remove a stuck drone top.   Drone bushings occasionally have small leaks, too.

Overall, a systematic approach will identify the source of your leak. 

If you didn't find a leak and you pipe is still hard to play, consider that perhaps your reeds are set to use too much air or that your blowstick is making you work too hard to get air into your pipes.